Control device for internal combustion engine

ABSTRACT

An internal combustion engine of the present invention is an internal combustion engine including a supercharger and an EGR device. Further, the internal combustion engine has an ISC passage that connects an upstream side and a downstream side of a throttle valve in an intake passage, and an ISC valve that regulates an amount of air that flows in the ISC passage. A control device of the present invention performs valve opening control that makes an opening degree of the ISC valve an opening degree larger than a reference opening degree when request torque required by the internal combustion engine is smaller than estimated torque that can be generated in the internal combustion engine, and prohibits opening of an EGR valve of the EGR device during execution of the valve opening control.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a national phase application based on the PCT International Patent Application No. PCT/JP2014/050140 filed Jan. 8, 2014, claiming priority to Japanese Patent Application No. 2013-066968 filed Mar. 27, 2013, the entire contents of both of which are incorporated herein by reference.

TECHNICAL FIELD

The invention relates to a control device for an internal combustion engine, and more particularly relates to a control device for an internal combustion engine including a bypass passage that connects an upstream side and a downstream side of a throttle valve, in an intake passage of the internal combustion engine.

BACKGROUND ART

Conventionally, there has been disclosed a control device for an internal combustion engine equipped with a supercharger, for example, in Patent Literature 1. Further, Patent Literature 1 proposes control of ignition timing for restraining an output variation that occurs when a target intake air that is set in response to request torque and an actual intake air amount differs. Specifically, the control device in Patent Literature 1 performs control of delaying ignition timing at a time of overshoot when an actual intake air amount is larger than a target intake air amount, and advancing the ignition timing at a time of undershoot when the actual intake amount is smaller than the target intake air amount.

CITATION LIST Patent Literatures

Patent Literature 1: Japanese Patent Laid-Open No. 2004-346917

Patent Literature 2: Japanese Patent Laid-Open No. 2012-102617

SUMMARY OF INVENTION Technical Problem

In the control of Patent Literature 1 described above, the output variation which occurs when the target intake air amount differs from the actual intake air amount is restrained by advancing or delaying the ignition timing. However, in the case of an internal combustion engine having a supercharger, the ignition timing is sometimes set at a delay side from MBT in a turbocharging region, in order to restrain knocking. In such a case, a margin up to a delay limit of the ignition timing is small. In such a case, it is conceivable that even if the actual intake air amount is larger than the target intake air amount, and reduction of the output torque is required, torque cannot be sufficiently reduced by only delay control of the ignition timing.

Here, in the case of an internal combustion engine having an ISC passage that connects an upstream side and a downstream side of the throttle valve, and having an ISC valve in the ISC passage, it is conceivable to open the ISC valve and cause the intake air to flow back to the upstream side from the ISC passage. Thereby, the amount of intake air that flows into the cylinder can be reduced, and the torque can be reduced.

However, with the control of opening the ISC valve like this, the intake air flows back through the ISC passage. Therefore, it is conceivable that depending on the operation state, the EGR rate deviates from a target value by backflow of the EGR gas, and combustion becomes instable.

The invention has an object to solve the above described problem, and provides a control device for an internal combustion engine that is improved to restrain combustion from becoming instable by realization of request torque by control of an ISC valve when there is a request to reduce output torque.

Means for Solving the Problems

In order to attain the above described object, a first invention is a control device for an internal combustion engine including a supercharger, including

an EGR device that recirculates part of an exhaust gas to an intake passage from an exhaust passage of the internal combustion engine, as an EGR gas,

a throttle valve that is installed in the intake passage,

an ISC passage that connects an upstream side and a downstream side of the throttle valve, in the intake passage,

an ISC valve that regulates an amount of air that flows in the ISC passage by being controlled to a predetermined opening degree,

control means for executing valve opening control that makes an opening degree of the ISC valve an opening degree larger than a reference opening degree, when request torque required by the internal combustion engine is smaller than estimated torque that can be generated in the internal combustion engine, and

means for prohibiting opening of an EGR valve of the EGR device, during execution of the valve opening control.

Here, “a reference opening degree” is desirably set at a maximum opening degree at which the ISC valve is fully opened, or a large opening degree close to the maximum opening degree.

A second invention further includes, in the first invention, means for closing the EGR valve before execution of the valve opening control, when there is an execution instruction of the valve opening control during opening of the EGR valve.

A third invention is such that, in the second invention,

the EGR device is a high-pressure-loop EGR device that recirculates part of the exhaust gas to the intake passage downstream from the compressor of the supercharger, from the exhaust passage upstream from the turbine of the supercharger.

A fourth invention further includes, in the second invention,

valve opening control prohibition means for prohibiting execution of the valve opening control, while the EGR gas remains in the intake passage after closing of the EGR valve.

A fifth invention is such that, in a third invention,

the EGR device is a low-pressure-loop EGR device that recirculates part of the exhaust gas to the intake passage upstream from the compressor of the supercharger, from the exhaust passage downstream from the turbine of the supercharger.

Advantageous Effect of Invention

At the time of valve opening control of the ISC valve, intake air flows back to the upstream side. Therefore, when the EGR valve is opened at the time of opening of the ISC valve, the EGR gas also flows back to the upstream side together with the intake air which flows back. Accordingly, it is conceivable that the EGR rate becomes larger than the EGR rate which is set as the target, and combustion becomes instable. In this regard, according to any of the first to the fifth inventions, opening of the EGR valve is prohibited during opening of the ISC valve. Thereby, even when the valve opening control of the ISC valve is performed, the EGR rate is made stable, and stabilization of combustion can be achieved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram for explaining an entire configuration of a system of embodiment 1 of the present invention.

FIG. 2 is a flowchart for explaining a routine of control that is executed by a control device in embodiment 1 of the present invention.

FIG. 3 is a flowchart for explaining a routine of control that is executed by the control device in embodiment 1 of the present invention.

FIG. 4 is a flowchart for explaining a routine of control that is executed by the control device in embodiment 1 of the present invention.

FIG. 5 is a schematic diagram for explaining an entire configuration of a system of embodiment 2 of the present invention.

FIG. 6 is a flowchart for explaining a routine of control that is executed by a control device in embodiment 2 of the present invention.

FIG. 7 is a schematic diagram for explaining an entire configuration of a system of embodiment 3 of the present invention.

FIG. 8 is a flowchart for explaining a routine of control that is executed by a control device in embodiment 3 of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that in the respective drawings, the same or corresponding parts will be assigned with the same reference signs and explanation thereof will be simplified or omitted.

Embodiment 1 Configuration of Embodiment 1

FIG. 1 is a schematic diagram for explaining a system configuration of embodiment 1 of the present invention. A system of the present embodiment includes a spark-ignition type internal combustion engine 2 to be a target of application of a control device. The internal combustion engine 2 uses gasoline as fuel, and can be preferably used as a power plant of a vehicle, for example. The internal combustion engine 2 can perform a stoichiometric combustion operation that combusts a mixture gas with an air-fuel ratio close to a theoretical air-fuel ratio (hereinafter, “stoichiometry”), and a lean combustion operation that combusts a mixture gas with an air-fuel ratio much leaner than the theoretical air-fuel ratio in a predetermined lean combustion operation region by switching between the stoichiometric combustion operation and the lean combustion operation. Further, FIG. 1 illustrates only one cylinder of the internal combustion engine 2, but the internal combustion engine 2 includes a plurality of cylinders. The number of cylinders and disposition of the cylinders of the internal combustion engine 2 are not specially limited.

Each of the cylinders of the internal combustion engine 2 is provided with a cylinder injector 4 and an ignition plug 6. The cylinder injectors 4 are installed to inject fuel into the respective cylinders of the internal combustion engine 2. In the configuration in FIG. 1, the cylinder injectors 4 are provided, but port injectors that inject fuel into intake ports may be used. Each of the cylinders of the internal combustion engine 2 is provided with an intake valve 8 and an exhaust valve 10. In the system, a variable valve mechanism (not illustrated) that controls opening and closing of the respective intake valves 8 and exhaust valves 10 is installed.

A downstream side end portion of an intake passage 12, and an upstream side end portion of an exhaust passage 14 respectively communicate with the respective cylinders. An air cleaner 20 is mounted in a vicinity of an inlet of the intake passage 12. An air flow meter 22 that outputs a signal corresponding to a flow rate of air that is taken into the intake passage 12 is provided in a vicinity of a downstream side of the air cleaner 20. A compressor 24 for turbocharger is installed downstream of the air flow meter 22.

An intercooler 26 that cools compressed air is provided downstream of the compressor 24 in the intake passage 12. An electronically controlled type throttle valve 28 is provided downstream of the intercooler 26. A surge tank 30 is provided downstream of the throttle valve 28.

The system in FIG. 1 has an ISC (Idle Speed Control) passage 32 that connects an upstream side of the throttle valve 28 and a downstream side of the throttle valve 28 in the intake passage 12. Specifically, one end of the ISC passage 32 is connected to a downstream side of the air cleaner 20 in the intake passage 12 and an upstream side of the compressor 24. The other end of the ISC passage 32 is connected to a downstream side of the surge tank 30, in the intake passage 12. In the ISC passage 32, an ISC valve 34 that opens and closes the ISC passage 32 is installed. The ISC valve 34 is a valve for changing a channel sectional area of the ISC passage 32 by an opening degree thereof being controlled to a predetermined opening degree, and regulating a flow rate of a gas flowing in the ISC passage 32.

In the exhaust passage 14, an exhaust turbine 36 of the turbocharger is installed. A catalyst 38 for purifying an exhaust gas is installed downstream of the exhaust turbine 36, and a muffler 40 is further installed downstream of the catalyst 38.

The system in FIG. 1 has a first pressure sensor 42 and a second pressure sensor 44. The first pressure sensor 42 is installed in a vicinity of a connection portion with the ISC passage 32, between the air cleaner 20 and the compressor 24 in the intake passage 12. By the first pressure sensor 42, a first pressure P1 that is an intake pressure in a vicinity of a connection portion of the ISC passage 32 and the intake passage 12 is acquired. The second pressure sensor 44 is installed in the surge tank 30. A second pressure P2 that is an intake pressure in the surge tank 30 is acquired based on an output of the second pressure sensor 44.

The system in FIG. 1 includes an ECU (Electronic Control Unit) 50. The control device of the present invention is realized as one function of the ECU 50. Various sensors for sensing an operation state of the internal combustion engine 2, such as the air flow meter 22 and the first and the second pressure sensors 42 and 44 described above are connected to the ECU 50. Further, various actuators that control the operation state of the internal combustion engine 2 such as the throttle valve 28, the cylinder injector 4 and the ignition plug 6 described above are connected to the ECU 50. The ECU 50 controls the operation state of the internal combustion engine 2 by executing a control program which is stored in a memory in advance, in accordance with parameters relating to the operation state of the internal combustion engine which are the result of acquiring the outputs of the respective sensors.

[Outline of ISC Valve Full Opening Control of Present Embodiment]

Control that is executed by the control device in the present embodiment includes control relating to an opening and a closing states of the ISC valve 34. In the control, the control device acquires request torque, and predicted generation torque (hereinafter, also called estimated torque) that is torque which can be generated in the internal combustion engine. The request torque and the predicted generation torque are calculated by a known method, and here, the calculation method is not limited. Further, the request torque and the predicted generation torque are not limited to the torque that is directly calculated by the control device in the present embodiment, but may be inputted by a system which is disposed at a higher rank than the control device.

The control device performs control of fully opening the ISC valve 34 under conditions that the predicted generation torque which is acquired is larger than the request torque, and that the second pressure P2 is larger than the first pressure P1. By fully opening the ISC valve 34 in the state in which the second pressure P2 at the downstream side of the intake passage 12 is larger than the first pressure P1 at the upstream side, the intake air is caused to flow back to the upstream side, and an internal pressure of the surge tank 30 can be reduced. Thereby, a torque variation in the case of the predicted generation torque is larger than the request torque is restrained. In the following embodiment, the valve opening control that fully opens the ISC valve 34 when the above described conditions (namely, the predicted generation torque is larger than the request torque, and the second pressure P2 is larger than the first pressure P1) are satisfied is also called “ISC valve full opening control”. Further, the conditions are also called “ISC valve fully opening conditions”.

FIG. 2 is a flowchart explaining a routine of control executed by the control device in embodiment 1 of the present invention. The routine in FIG. 2 is a routine that is repeatedly executed at each set time interval during an operation of the internal combustion engine 2. In the routine in FIG. 2, it is firstly determined whether or not an ISC valve full opening prohibition flag is cleared (S10). The ISC valve full opening prohibition flag is a flag which is switched to be set and cleared by processing that will be described later, and while the flag is set, the ISC valve full opening control is prohibited. Accordingly, when it is not recognized that the ISC valve full opening prohibition flag is cleared in step S10, the current process is temporarily ended.

When it is recognized that the ISC valve full opening prohibition flag is cleared in step S10, the request torque is acquired next (S12). Next, an engine control target value is acquired (S14). The engine control target value is, for example, a target opening degree of the throttle valve 28, target ignition timing, a target opening degree of the ISC valve 34 and the like which are set at present. Next, the predicted generation torque is calculated in accordance with these control target values (S16).

Next, it is determined whether or not the predicted generation torque which is calculated in step S16 is larger than the request torque which is acquired in step S12 (S18). When it is not recognized that the predicted generation torque is larger than the request torque in step S18, the current process is temporarily ended.

When it is recognized that the predicted generation torque is larger than the request torque in step S18, it is determined whether or not the second pressure P2 is larger than the first pressure P1 next (S20). When it is not recognized that the second pressure P2 is larger than the first pressure P1 in step S20, the current process is ended.

When it is recognized that the second pressure P2 is larger than the first pressure P1 in step S20, the ISC valve 34 is fully opened (S22). The ISC valve 34 is fully opened in the state in which the second pressure P2 is larger than the first pressure P1, whereby part of intake air flows through the ISC passage 32 and flows back to the upstream side of the intake passage 12 from the downstream side from the surge tank 30 of the intake passage 12. Thereby, the surge tank internal pressure is reduced, and torque is restrained. Thereafter, the current process is ended.

[Outline of Control of Prohibiting Lean Combustion Operation of Present Embodiment]

Incidentally, the internal combustion engine 2 of the present embodiment is an internal combustion engine capable of a lean combustion operation. In the case of the internal combustion engine capable of a lean combustion operation like this, the intake port shapes are optimized to perform lean combustion stably, and are designed to enhance swirl flows and tumble flows that occur in the cylinders. However, during execution of the ISC valve full opening control, the intake air flows back to the upstream side via the ISC passage 32. Therefore, during the ISC valve full opening control, the flow of the intake air in the intake passage 12 also changes significantly. As a result, the swirl flows and the tumble flows which occur in the cylinders become insufficient, and it is conceivable that the lean combustion limit is lowered, or lean combustion becomes unstable in particular.

Accordingly, in the present embodiment, the control device executes control of prohibiting a lean combustion operation during the ISC valve full opening control. FIG. 3 is a flowchart for explaining a routine of control executed by the control device in embodiment 1 of the present invention. The routine in FIG. 3 is a routine that is repeatedly executed at each set time interval during an operation of the internal combustion engine 2. In the routine in FIG. 3, it is firstly determined whether or not the ISC valve full opening control is under execution (S102). When it is recognized that the ISC valve full opening control is under execution in step S102, a target air-fuel ratio is set at stoichiometry (S104). Thereby, a lean combustion operation is prohibited. Thereafter, the current process is ended.

When it is not recognized that the ISC valve full opening control is under execution in step S102, it is determined whether or not the condition of the lean combustion operation is established at present in S106. The lean combustion operation condition is stored in the control device in advance. More specifically, the condition that the engine speed of the internal combustion engine 2 is equal to or smaller than the predetermined speed, for example, or the like is cited.

When establishment of the lean combustion operation condition is not recognized in step S106, the flow proceeds to step S104, and the target air-fuel ratio is set at stoichiometry. Thereafter, the current process is ended.

When establishment of the lean combustion operation condition is recognized in step S106, the target air-fuel ratio is set at a predetermined lean air-fuel ratio next (S108). Thereafter, the current process is ended.

By the above process, a lean combustion operation is prohibited during execution of the ISC valve full opening control, and a stoichiometric combustion operation is executed. Thereby, stabilization of combustion during the ISC valve full opening control can be achieved.

[Outline of Prohibition Control of ISC Valve Full Opening Control of Present Embodiment]

Further, the control device of the present embodiment prohibits the ISC valve full opening control at the time of a lean combustion operation. That is to say, when the lean combustion operation is performed, the ISC valve full opening control is not performed even in an operation state in which the ISC valve full opening conditions are established.

FIG. 4 is a flowchart for explaining a routine of control executed by the control device in embodiment 1 of the present invention. The routine in FIG. 4 is a routine that is repeatedly executed at each set time interval during an operation of the internal combustion engine 2. In the routine in FIG. 4, it is firstly determined whether or not the internal combustion engine 2 is under a lean combustion operation (S112).

When it is recognized that the internal combustion engine 2 is under a lean combustion operation in step S112, the ISC valve full opening prohibition flag is set next (S114). The ISC valve full opening prohibition flag is a flag that is used in determination of whether or not the ISC valve full opening control can be executed in step S10 in the routine in FIG. 2 described above, and by the flag being set, the ISC valve full opening control by the routine in FIG. 2 is prohibited. Thereafter, the current process is ended. In this case, the ISC valve 34 is controlled in accordance with a control program at a normal time of the ISC valve 34 which is stored in the ECU 50 separately. The ISC valve full opening control is prohibited at the time of a lean combustion operation by the process. However, even during a lean combustion operation, the ISC valve 34 is opened by the control flag at the normal time, and is fully opened in some cases.

When it is not recognized that the internal combustion engine is under a lean combustion operation at present in step S112, the ISC valve full opening prohibition flag is cleared (S116). Thereby, execution of the routine in FIG. 2 is permitted, and when the ISC valve full opening conditions which are determined in the routine in FIG. 2 are established, the ISC valve 34 is fully opened. Thereafter, the current process is ended.

As described above, according to the present embodiment, during execution of the ISC valve full opening control, switching to the lean combustion operation is prohibited, whereas during the lean combustion operation, the ISC valve full opening control is prohibited. Thereby, while stable combustion is ensured in the lean combustion operation region, torque variation can be restrained outside the lean combustion operation region.

In the present embodiment, the case is described, in which the opening degree of the ISC valve 34 is made full opening which is a maximum opening degree when the ISC valve full opening conditions are established. However, the present invention is not limited thereto, and the opening degree of the ISC valve 34 may be made larger than a predetermined reference opening degree. Here, the reference opening degree can be properly set at such a large opening degree that can reduce generation torque by causing the intake air to flow back early by opening the ISC valve. This similarly applies to other embodiments.

Further, the case is described, in which the system of the present embodiment includes the first pressure sensor 42 and the second pressure sensor 44, and acquires the first pressure P1 and the second pressure P2 based on the outputs from these sensors. However, the present invention may have a configuration that does not have both or one of the first pressure sensor 42 and the second pressure sensor 44. In the case like this, estimated values of the pressures of the respective portions can be used as the first pressure P1 and the second pressure P2. This similarly applies to other embodiments.

Further, in the present embodiment, the case is described, in which the control device executes both the routines in FIG. 3 and FIG. 4, and thereby prohibits switching to the lean combustion operation during the ISC valve full opening control, and prohibits execution of the ISC valve full opening control during the lean combustion operation. However, the present invention is not limited to the one that executes both the controls, but may be the one that performs only one control. This similarly applies to other embodiments.

Embodiment 2

FIG. 5 is a diagram for explaining a system in embodiment 2 of the present invention. As shown in FIG. 5, the system in FIG. 5 has the same configuration as the system in FIG. 1, except that the system in FIG. 5 has a high-pressure-loop EGR device. More specifically, the system in FIG. 5 has a high-pressure-loop EGR (HPL-EGR; High Pressure Loop-Exhaust Gas Recirculation) device that recirculates part of an exhaust gas to the intake passage 12 from the exhaust passage 14 as an EGR gas, in addition to the system in FIG. 1.

The high-pressure-loop EGR device has high-pressure-loop EGR piping 60, a high-pressure-loop EGR cooler 62 and a high-pressure-loop EGR valve 64 which are provided in the high-pressure-loop EGR piping 60. The high-pressure-loop EGR piping 60 has one end thereof connected to an upstream side from the exhaust turbine 36 in the exhaust passage 14, and has the other end connected to between the surge tank 30 and an intake manifold (not illustrated) in the intake passage 12. The high-pressure-loop EGR valve 64 is a valve that can change a channel sectional area of the high-pressure-loop EGR piping 60 by an opening degree thereof being regulated. That is to say, a flow rate of the EGR gas which flows in the high-pressure-loop EGR piping 60 is controlled by control of the opening degree of the high-pressure-loop EGR valve 64.

The control device controls the opening degree of the EGR valve 64 by issuing a control signal to control the opening degree of the high-pressure-loop EGR valve 64 in accordance with a control program that is stored in advance. Incidentally, it is conceivable that if the ISC valve full opening control is executed during use of the high-pressure-loop EGR, an unpurified EGR gas flows back to the air cleaner 20 side via the ISC passage 32, and stays in the air cleaner 20 or is released into the atmosphere.

Therefore, in the present embodiment, the control device includes control of prohibiting the ISC valve full opening control during opening of the high-pressure-loop EGR valve. More specifically, the control device of embodiment 2 fully closes the high-pressure-loop EGR valve 64 when there is an execution instruction of the ISC valve full opening control in a state in which the high-pressure-loop EGR valve 64 is opened, and thereafter, the control device executes the ISC valve full opening control.

FIG. 6 is a flowchart for explaining a routine of the control executed by the control device in embodiment 2 of the present invention. The routine in FIG. 6 is a routine which is executed in place of the routine in FIG. 2, and is repeatedly executed at fixed time intervals. The routine in FIG. 6 is the same as the routine in FIG. 2 except for a point having processes in steps S202 to S206 between the process in step S20 and the process in step S22 in the routine in FIG. 2.

When establishment of the ISC valve full opening conditions is recognized in the processes up to and in S20, it is firstly determined whether or not the high-pressure-loop EGR valve 64 is opening, after the process in S20 (S202), in the routine in FIG. 6.

When it is determined that the high-pressure-loop EGR valve 64 is opening in step S202, a control signal that fully closes the high-pressure-loop EGR valve 64 is issued next (S204). Next, it is determined whether or not the high-pressure-loop EGR valve 64 is fully closed (S206). That is to say, it is confirmed whether or not the high-pressure-loop EGR valve 64 is fully closed actually by the control instruction in step S204. When it is not recognized that the high-pressure-loop EGR valve 64 is closed in step S206, the current process is ended as it is. That is to say, the ISC valve 34 is not fully opened, and the current process is ended.

When full closure of the high-pressure-loop EGR valve 64 is recognized in step S206, or when it is determined that the EGR valve is not opening in step S202, the ISC valve full opening control is executed next (S22). Thereafter, the current process is ended.

As described above, in the present embodiment, the ISC valve full opening control is prohibited while the high-pressure-loop EGR valve 64 is opened, and even when the ISC valve full opening control conditions are established, the ISC valve full opening control is executed after the high-pressure-loop EGR valve 64 is closed. Thereby, backflow of the unpurified EGR gas can be restrained, and combustion can be restrained from becoming instable as a result the EGR rate increases by the EGR gas which stays in the air cleaner 20. Further, the unpurified EGR gas can be restrained from being released outside the intake port by backflow, and worsening of emission can be prevented.

In the present embodiment, the case of performing the control relating to the lean combustion operation described in embodiment 1 and the control relating to the high-pressure-loop EGR valve of the present embodiment in combination is explained. That is to say, according to the routine in FIG. 6, the ISC valve full opening prohibition flag is set during the lean combustion operation in the routine in FIG. 4. Therefore, execution of the ISC valve full opening control is prohibited by the process in S10, and execution of the ISC valve full opening control is prohibited during opening of the EGR valve 64 by the processes in S202 to S206. Furthermore, the routine in FIG. 3 is executed in combination, whereby the lean combustion operation during the ISC valve full opening control is prohibited. This similarly applies to other embodiments.

However, the present invention is not limited to the above, and both or one of the prohibition control of the ISC valve full opening control at the time of the lean combustion operation in embodiment 1 and the prohibition control of the lean combustion operation during the ISC valve full opening control do or does not have to be combined. In the case like this, determination of whether or not the ISC valve full opening prohibition flag is cleared in step S10 in the routine in FIG. 6 and/or the routine in FIG. 3 can be omitted, for example. This similarly applies to other embodiments.

In the present embodiment, the processes in steps S12 to S20 and S22 in FIG. 6 are executed, whereby “control means for executing valve opening control” of the present invention is realized, the processes in steps S202 to S206 are executed, whereby “means for prohibiting opening of the EGR valve” of the present invention is realized, and the process in step S204 is executed, whereby “means for closing the EGR valve” is realized.

Embodiment 3

FIG. 7 is a diagram for explaining an entire configuration of a system of embodiment 3 of the present invention. The system in FIG. 7 is the same as the system in FIG. 1 except for the point having a low-pressure-loop EGR device. The system in FIG. 7 has a low-pressure-loop EGR device (LPL-EGR: Low Pressure Loop-Exhaust Gas Recirculation) device.

In the system in FIG. 7, the low-pressure-loop EGR device has low-pressure-loop EGR piping 66, and a low-pressure-loop EGR cooler 68 and a low-pressure-loop EGR valve 70 which are provided in the low-pressure-loop EGR piping 66. The low-pressure-loop EGR piping 66 has one end thereof connected to a downstream side from the catalyst 38 in the exhaust passage 14, and the other end connected to an upstream side from the compressor 24, in the intake passage 12. The low-pressure-loop EGR valve 70 is a valve that can change the channel sectional area of the low-pressure-loop EGR piping 66 by an opening degree thereof being regulated. That is to say, the flow rate of the EGR gas which flows in the low-pressure-loop EGR piping 66 is controlled by control of the opening degree of the low-pressure-loop EGR valve 70.

As shown in FIG. 7, in the case of the low-pressure-loop EGR device, one end of the low-pressure-loop EGR piping 66 is connected to the upstream side from the compressor 24 in the intake passage 12. Accordingly, even when recirculation of the EGR gas by the low-pressure-loop EGR device is stopped, a residence time period of the EGR gas, which remains in the intake passage 12 after closure of the low-pressure-loop EGR valve 70, becomes longer as compared with the case of the high-pressure-loop EGR device. Accordingly, even when the low-pressure-loop EGR valve 70 is closed, if the ISC valve full opening control is executed in the state in which the EGR gas remains in the intake passage 12, there is the fear of the remaining EGR gas flowing back to the air cleaner 20 side and being discharged outside.

Therefore, in the present embodiment, the EGR gas residual amount in the intake passage 12 after closure of the low-pressure-loop EGR valve 70 is estimated, and when it is recognized that the remaining EGR is eliminated, control of permitting full opening of the ISC valve is performed. Here, the EGR gas residual amount is obtained in accordance with a piping capacity downstream of the low-pressure-loop EGR valve 70, the flow rate of the intake air and the like.

FIG. 8 is a flowchart for explaining a routine of control executed by the control device in embodiment 3 of the present invention. The routine in FIG. 8 is a routine that is executed at fixed time intervals in place of the routine in FIG. 6. The routine in FIG. 8 is the same as the routine in FIG. 2 except for a point having processes in steps S302 to S308 between steps S20 and S22.

In the routine in FIG. 8, when establishment of the ISC valve full opening conditions is recognized by the processes up to and including step S20, it is determined whether or not the low-pressure-loop EGR valve 70 is opening (S302). When it is recognized that the low-pressure-loop EGR valve 70 is opening in step S302, the low-pressure-loop EGR valve 70 is fully closed next (S304). The control device closes the low-pressure-loop EGR valve 70 by issuing a predetermined control signal.

When the low-pressure-loop EGR valve 70 is fully closed in step S304, or when it is not recognized that the low-pressure-loop EGR valve 70 is opening in step S302, an EGR gas residual amount is calculated next (S306). Here, the EGR gas residual amount is an amount of the EGR gas remaining in the intake passage 12 at a time point of calculation, and is obtained in accordance with an arithmetic operation formula or the like that is stored in the control device in advance in response to an elapsed time period, and an intake air amount after the low-pressure-loop EGR valve 70 is closed, and a capacity of the intake passage 12 downstream of the low-pressure-loop EGR valve 70 and the like.

Next, it is determined whether or not the EGR gas residual amount calculated in step S306 is equal to or smaller than zero (S308). When it is not recognized that the EGR gas residual amount is equal to or smaller than zero, the cuiTent process is ended as it is. That is to say, it is determined that the EGR gas remains in the intake passage 12 although it is the state in which establishment of the ISC valve full opening control execution conditions is recognized by the processes up to and in S20, and therefore, the ISC valve is not fully opened, but the current process is ended as it is temporarily, after which, the routine in FIG. 8 is repeated again.

When it is recognized that the EGR gas residual amount is equal to or smaller than zero in step S308, the ISC valve 34 is fully opened next (S22). Thereafter, the current process is ended.

As described above, according to the present embodiment, in the case of using the low-pressure-loop EGR device, full opening of the ISC valve is prohibited while the EGR gas remains even after closure of the low-pressure-loop EGR valve 70. Accordingly, the EGR gas can be more reliably prevented from flowing back from the ISC passage 32 and being released outside from the air cleaner 20.

In the present embodiment, the case of having only the low-pressure-loop EGR device as the EGR device is described. However, the present invention is not limited to this, and may be the one also having the high-pressure-loop EGR device described with FIG. 5. In this case, control relating to the high-pressure-loop EGR may be executed as described in embodiment 2, in accordance with the routine in FIG. 6. Further, with respect to the high-pressure-loop EGR device, the residual amount of the EGR gas after valve closure is calculated, and at the time point when the residual amount becomes zero, full opening of the ISC valve may be performed, as described in the routine in FIG. 8. This similarly applies to the other embodiments.

Further, concerning embodiment 3, the case is described, in which the control relating to the lean combustion operation in embodiment 1, and the control concerning the low-pressure-loop EGR valve in the present embodiment are combined. That is to say, according to the routine in FIG. 8, execution of the ISC valve full opening control is prohibited during the lean combustion operation by the process in S10, and while the EGR gas remains by the processes in S302 to S308, execution of the ISC valve full opening control is prohibited. Further, the routine in FIG. 3 is executed in combination, whereby the lean combustion operation during the ISC valve full opening control is prohibited. This similarly applies to the other embodiments.

However, the present invention is not limited to the above, and both or one of the prohibition control of the ISC valve full opening control at the time of the lean combustion operation in embodiment 1 and the prohibition control of the lean combustion operation during the ISC valve full opening control do or does not have to be performed in combination. In the case like this, determination of whether or not the ISC valve full opening prohibition flag is cleared in step S10 in the routine in FIG. 8 and/or the routine in FIG. 3 can be omitted, for example. This similarly applies to the other embodiments.

In the present embodiment 3, the processes in steps S12 to S20 and S22 in FIG. 8 are executed, whereby “control means for executing valve opening control” of the present invention is realized, the processes in steps S302 to S304 are executed, whereby “means for prohibiting opening of the EGR valve” of the present invention is realized, and the process in step S304 is executed, whereby “means for closing the EGR valve” is realized, and the processes in steps S306 to S308 are executed, whereby “valve opening control prohibition means” is realized.

When the numerals of the numbers, the quantities, the amounts, the ranges and the like of the respective elements are mentioned in the above embodiment, the present invention is not limited by the mentioned numerals, unless explicitly mentioned otherwise, or unless clearly specified by the numerals theoretically. Further, the structures, the methods and the like explained in the embodiment are not always essential to the invention, unless explicitly mentioned otherwise, or unless clearly specified by the structures, the methods and the like theoretically.

DESCRIPTION OF REFERENCE CHARACTERS

-   2: Internal combustion engine -   4: cylinder injector -   6: ignition plug -   8: intake valve -   10: exhaust valve -   12: intake passage -   14: exhaust passage -   20: air cleaner -   22: air flow meter -   24: compressor -   26: intercooler -   28: throttle valve -   30: surge tank -   32: ISC passage -   34: ISC valve -   36: exhaust turbine -   38: catalyst -   40: muffler -   42: first pressure sensor -   44: second pressure sensor -   50: ECU -   60: high-pressure-loop EGR piping -   62: high-pressure-loop EGR cooler -   64: high-pressure-loop EGR valve -   66: low-pressure-loop EGR piping -   68: low-pressure-loop EGR cooler -   70: low-pressure-loop EGR valve 

The invention claimed is:
 1. A control device for an internal combustion engine including a supercharger, the supercharger comprising a compressor installed in an intake passage and a turbine disposed in an exhaust passage, comprising: a high-pressure-loop exhaust gas recirculation (EGR) piping that connects the intake passage downstream from the compressor and the exhaust passage upstream from the turbine; a high-pressure-loop EGR valve that is installed in the high-pressure-loop EGR piping; a throttle valve that is installed in the intake passage; an idle speed control (ISC) passage that connects an upstream side and a downstream side of the throttle valve, in the intake passage; an ISC valve that regulates an amount of air that flows in the ISC passage by being controlled to a predetermined opening degree; and an electronic control unit, wherein the electronic control unit is configured to: control an opening degree of the ISC valve to be larger than a reference opening degree, when request torque required by the internal combustion engine is smaller than a predicted generation torque calculated in accordance with control target values which are set at present; and prohibit opening of the high-pressure-loop EGR valve, during execution of the ISC valve opening control.
 2. The control device for an internal combustion engine according to claim 1, wherein the electronic control unit is configured to: close the high-pressure-loop EGR valve before execution of the ISC valve opening control when there is an execution instruction of the ISC valve opening control during opening of the high-pressure-loop EGR valve.
 3. The control device for an internal combustion engine according to claim 2, wherein the electronic control unit is configured to: prohibit execution of the ISC valve opening control, while EGR gas remains in the intake passage after closing of the high-pressure-loop EGR valve.
 4. A control device for an internal combustion engine including a supercharger, the supercharger comprising a compressor installed in an intake passage and a turbine disposed in an exhaust passage, comprising: a low-pressure-loop exhaust gas recirculation (EGR) piping that connects the intake passage upstream from the compressor and the exhaust passage downstream from the turbine; a low-pressure-loop EGR valve that is installed in the low-pressure-loop EGR piping; a throttle valve that is installed in the intake passage; an idle speed control (ISC) passage that connects an upstream side and a downstream side of the throttle valve, in the intake passage; an ISC valve that regulates an amount of air that flows in the ISC passage by being controlled to a predetermined opening degree; and an electronic control unit, wherein the electronic control unit is configured to: control an opening degree of the ISC valve to be larger than a reference opening degree, when request torque required by the internal combustion engine is smaller than a predicted generation torque calculated in accordance with control target values which are set at present; and prohibit opening of the low-pressure-loop EGR valve during execution of the ISC valve opening control.
 5. The control device for an internal combustion engine according to claim 4, wherein the electronic control unit is configured to: close the low-pressure-loop EGR valve before execution of the ISC valve opening control when there is an execution instruction of the ISC valve opening control during opening of the low-pressure-loop EGR valve.
 6. The control device for an internal combustion engine according to claim 5, wherein the electronic control unit is configured to: prohibit execution of the ISC valve opening control, while EGR gas remains in the intake passage after closing of the low-pressure-loop EGR valve. 